Activity datafields only exist for the duration of the activity.  You cannot reference the activity-level data fields outside of the activity. For your second question: K2.ActivityInstanceDestination.DataFields[''myData''].Value is a data field associated with the current slot in the current activity ...

What I would like to do is display an item's 'due date' in the SharePoint worklist web part, so the user can sort by when items are due with more granularity than just the priority of the items.  The due date of an activity is custom based on an xml data field (some processes are 30 days before this value, others 40 days, etc.).  I can ...